1. Field of the Invention
The present invention relates to printers which print characters on the pages which are exposed when a book is opened, such as a diary, notebook, passbook, passport, loose leaf book, etc. The present invention relates to apparatus and methods for printing on a book which typically has a bound portion by which a plurality of sheets are bound together.
2. Description of the Related Art
A passbook printer has been used which prints directly on the passbook including sheets or pages bound at their edge by feeding the passbook in the direction along the bound portion. In the opened condition, the thickness of the left side pages of the passbook usually differs from the thickness of the right side pages whereas both the thickness are substantially equal when the passbook is opened at a middle page. The terms "left and right pages" used in conjunction with the description of the present invention means the left side portion and the right side portion of the bound portion of the opened passbook. In addition, the thickness of the left side pages, for example, means a total thickness or height of the left side which is determined by the number of stacked sheets of the left side along with the book cover and jacket, if any. Prior art printers for feeding the passbook along the parallel direction to the bound portion have used one of the following two typical feeding mechanisms.
In the first feeding mechanism, one rotating shaft extending, in a perpendicular direction to the direction of the bound portion is mounted above the opened passbook, and one end of the rotating shaft is pivotally supported. The angle between the rotating shaft and the direction of the bound portion is maintained at 90-degrees, and the other end of the pivoted rotating shaft can be moved towards, or away from, the opened passbook. A plurality of feeding rollers made of sponge are fixed on the rotating shaft. In the case wherein the height of both the pages differs from each other, the rotating shaft is inclined, but the rollers are compressed in an effort to maintain engagement with the pages.
In this feeding scheme, however, when the difference of the heights of the left side pages and the right side pages becomes large, the feeding force to the right side pages becomes different from the feeding force to the left side pages. Accordingly, feeding of the passbook in a manner truly parallel to the direction of the bound portion is not performed.
In the second feeding mechanism, one rotating shaft, extending in a perpendicular direction to the direction of the bound portion, is mounted above the opened passbook, and both the ends of the rotating shaft are so supported that both the ends are moved in upward and downward directions, whereby the rotating shaft is moved parallel to the surfaces of both the pages while keeping an angle of 90-degrees to the direction of the bound portion. A plurality of feeding rollers are fixed on the rotating shaft. In this feeding mechanism, however, the rotating shaft is inclined against the left and right pages when the difference of the height of the left side pages and the right side pages becomes large, as in the case of the first mechanism mentioned above. Accordingly, the feeding forces of all the rollers cannot be equal.